1. Field of the Invention
This invention relates to physiological function-enhancing agents to be used for the treatment of tumors, which comprise a compound capable of stimulating the generation of at least one type of active oxygen, such as superoxide radicals and singlet oxygen, by the chemical action caused by irradiation of ultrasonic waves.
2. Description of the Prior Art
As physical methods used for the treatment of solid cancers, radiotherapy (irradiation of X-rays and .gamma.-rays), thermotherapy, laser irradiation and ultrasonic irradiation are known.
Of these, radiotherapy has the disadvantage that sufficient doses to ensure the complete cure of cancers cannot be actually applied because normal tissues are also affected by the irradiation; thermotherapy is no more than an aid to other therapeutical methods; and laser irradiation (a recently developed technique) is poor in the degree of penetration, and hence little effect can be expected except for the treatment of cancers in surface tissues.
Ultrasonic irradiation, on the other hand, is superior to radiotherapy in that the applied waves can be focused solely on the cancer tissues to be treated with little effect upon normal tissues, and is better than laser irradiation in the degree of penetration.
However, application of ultrasonic irradiation for the treatment of cancers has hitherto aimed principally at the destruction of cancer tissues by the physical effects of ultrasonic waves and at the thermotherapeutic effects by its pyretic action, and these effects have been unsatifactory for the complete cure of cancers. As a result, cases are very few in which ultrasonic irradiation was actually applied to the treatment of cancers, despite its better characteristics compared with the other types of physiotherapy.
The present inventors formerly attempted a combination of ultrasonic irradiation with administration of an anthracycline antitumor agent (e.g., adriamycin), and reported the experimental results on their additive or synergistic effects [Japan Hyperthermia, 3 (2), 175-182].
This method proved effective in treating cancers, but is still far from ideal because of the limited dose of antitumor agent as almost all of such drugs have toxicity to a greater or lesser extent.